Isostatic molding is a pressing process for densifying a powdered composition into a compact shape at pressures sufficient to obtain near theoretical density. Powder and particulate matter is densified under pressure acting through a suitable fluid medium preferably a liquid to achieve an omnidirectional high green density.
Current state of the art isostatic molding recognizes that density more than any other property influences the final mechanical and physical properties of the pressed material. Density determines the strength and physical properties of the compact billet both in the green and final sintered state. In current practice the green density level of the compressed product is indirectly controlled during the molding operation by setting a target pressure and controlling the rate of pressurization of the press until the target pressure is realized. Secondary process variables also include: temperature, hold time under compression mold filling techniques, and depressurization controls. Unfortunately, experience has shown that product uniformity, particularly for a carbon or ceramic composite cannot be achieved with a high degree of accuracy by control of pressure with or without adjustment of the other indicated process variables. Instead, a wide range of variability in the characteristics of the product is found to exist due to non-uniformity in product density. To guarantee product repeatability particularly for graphite and ceramic products, the product density must be held to within a limited narrow range of density.